code: def forward(self, x):
      return self.ffn(x)
  
file_path: fairscale/tests/nn/data_parallel/test_fsdp_with_checkpoint_wrapper.py
imports: import contextlib
  import pytest
  import torch
  from torch import nn
  import torch.distributed
  import torch.multiprocessing
  from fairscale.fair_dev.testing.testing import dist_init, skip_if_single_gpu, teardown, temp_files_ctx
  from fairscale.nn.checkpoint.checkpoint_activations import checkpoint_wrapper
  from fairscale.nn.data_parallel import FullyShardedDataParallel
label_desc: Use image node_id 2 for calling the SimpleModuleWithCheckpointing obj's underlying member method code with example usage: obj.forward(x) and returns: self